AU2011379051A1

AU2011379051A1 - Stack assembly

Info

Publication number: AU2011379051A1
Application number: AU2011379051A
Authority: AU
Inventors: Jacob BREINER; Niels Erikstrup; Martin Refslund Nielsen
Original assignee: Haldor Topsoe AS
Current assignee: Topsoe AS
Priority date: 2011-10-14
Filing date: 2011-10-14
Publication date: 2014-05-01
Also published as: CN103875111B; CA2851718A1; US20140234744A1; DK2766947T3; ES2590341T3; HK1199150A1; WO2013053374A1; US9865896B2; KR101899114B1; EP2766947B1; EA201490791A1; CN103875111A; EP2766947A1; KR20140084173A; IN2014CN02745A

Abstract

A solid oxide fuel or solid oxide electrolysis cell Stack assembly (203) has an improved, simple, cost reducing and robust compression System, housing and Single sided System interface with a flexible - interface - fixture (204) which is rigid enough to fix the at least one cell Stack in the housing when not in Operation, but flexible enough to allow for transfer of the compression force from the flexible compression mat (211) in the top closed end of the housing (201), through the at least one cell Stack and further towards the interface counterpart of the System when in Operation.

Description

WO 2013/053374 PCT/EP2011/005165 Title: Stack Assembly The invention relates to an assembly for a solid oxide fuel cell (SOFC) stack or a solid oxide electrolysis cell (SOEC) 5 stack, more specifically to an enclosing casing, which pro vides protection and compression for such a stack and an improved interface for connection of the assembly to an SOFC or an SOEC system. 10 The present invention relates to features outside the stack itself, and it can be used for both SOFC and SOEC. In the following the invention will however mainly be explained in relation to SOFC for the sake of simplicity. In the follow ing often the SOFC stack or the SOEC stack will be referred 15 to as merely the cell stack. The electro-chemical reactions and the function of a fuel cell is not the essence of the present invention, thus this will not be explained in detail, but considered known for a 20 person skilled in the art. To increase the voltage produced by the SOFC, several cell units are assembled to form a stack and are linked together by interconnects. These layers of the stack are sealed to 25 gether with a gas tight and temperature resistant seal such as glass along some or all edges. The interconnects serve as a gas barrier to separate the anode (fuel) and cathode (air/oxygen) sides of adjacent cell units, and at the same time they enable current conduction between the adjacent 30 cells, i.e. between an anode of one cell with a surplus of electrons and a cathode of a neighbouring cell needing electrons for the reduction process. The current conduction CONFIRMATION COPY WO 2013/053374 PCT/EP2011/005165 2 between the interconnect and its neighbouring electrodes is enabled via a plurality of contact points throughout the area of the interconnect. The contact points can be formed as protrusions on both sides of the interconnect. The effi 5 ciency of the fuel cell stack is dependant of good contact in each of these points, and therefore it is crucial that a suitable compression force is applied to the fuel cell stack. This compression force must be large enough and evenly distributed throughout the area of the fuel cell to 10 ensure electrical contact, but not so large that it damages the electrolyte, the electrodes, the interconnect or im pedes the gas flow over the fuel cell. The compression of the fuel cell is also vital for the seal between the layers of the stack to keep the stack gas tight. 15 The present invention relates to cell stacks with both in ternal manifolding and stacks with external (side) mani folding. By internal manifolding is meant that the process gas distribution from a gas inlet or outlet to or from each 20 of the cells in the cell stack is provided by a manifold which is located physically within / integrated in the sub stantially box shaped cell stack, whereas external mani folding means that the process gas distribution from a gas inlet or outlet to or from each of the cells in the cell 25 stack is provided by a manifold which is located physically outside, adjacent to the substantially box shaped cell stack. Though external manifolded cell stacks have a higher per 30 formance than internal manifolded cell stacks they require gas manifolds that lead the gas to and away from the cell stack. Obtaining sealing with small leakages of the exter- WO 2013/053374 PCT/EP2011/005165 3 nal manifolds is a known technical problem, a problem which is important to solve, since gas leakages have a negative impact on the system efficiency. 5 External manifolded cell stacks normally have an interface that is difficult to connect to a solid oxide fuel cell (or solid oxide electrolysis cell) system. By solid oxide fuel cell system (or solid oxide electrolysis cell system) is meant the surrounding parts necessary for the cell stack to 10 operate, i.e. process gas pre-treatment (air-blowers, heat exchangers, gas reformers etc.) and delivery, process gas withdrawal and after-treatment, electrical power take-out, thermal insulation, vibration damping, measuring equipment etc. This is caused by the fact that external manifolded 15 cell stacks normally have the process gas connections on three different sides of the substantially box shaped cell stack. Often these results in manifold designs where four tubes need individual fitting with gaskets, clamps or like wise to the solid oxide fuel cell system's tubing. This 20 kind of tube connections results in several problems: e Tube connections occupy space consuming and result in larger solid oxide fuel cell systems. Larger solid ox ide fuel cell systems result in bigger heat loss, lar 25 ger amount of necessary thermal insulation, and in general larger production costs. In addition to this, compactness is an important parameter in order to fit the solid oxide fuel cell system in products with a limited amount of space e.g. trucks. 30 e In order to be able to mount and obtain a long life and a tight fit to all of the tube connections, com- WO 2013/053374 PCT/EP2011/005165 4 pensators need to be fitted to all or some of the tubes to make up for relative dimension deviations from tube to tube caused by manufacturing and/or dif ferences in thermal expansion due to operation condi 5 tions. This is a problem since compensators are expen sive, mechanically fragile, thin walled, take up space and have a large heat loss. e The risk of a malfunction (leakage) increases with the 10 number of connections. " Four individual fittings are time consuming to mount. * Known tube connections can be difficult to loosen up 15 after use, as metal parts tend to seize together. Manifolds and compression arrangements often require a large number of parts. This increases the risk of malfunc tion and total costs. 20 Compression arrangements are known to be cumbersome when installing cell stacks. Many compression arrangements re quire a shift from one compression arrangement to another when the cell stack is installed in a system. The overlap 25 ping of the forces from the two compression arrangements makes it difficult to stay in the desired compression force interval. This installation is often done manually and is time consuming, cumbersome and contains the risk of provid ing too much compression force, too little compression 30 force and/or a bad distribution of the compression force. In addition to this; failure in compression arrangements is a known source of error in fuel cell systems.

WO 2013/053374 PCT/EP2011/005165 5 It is known that SOFC and SOEC system start up time can be reduced by reducing system and stack mass. Electric short circuiting is a known failure mode. The cell 5 stack sides are charged with an electrical potential rela tive to the rest of the system and hence they are vulner able regarding electrical short circuiting. The electri cally positive side of the fuel cell stack must also be protected from short circuiting 10 If a malfunction of a fuel cell stack occurs, fuel leakages can result in a safety problem. A serious malfunction of the cell stack can melt the cell stack and might damage surrounding components. 15 A solution to some of these problems has been proposed in US 2010143814, which is concerned with improved fuel cell stack assemblies, and methods of operation of a fuel cell stack assembly, particularly with improved gas flow and 20 thermal management. In DE10124853 a unit has a sealed housing in which there is a stack of fuel cells. During operation the cells are fed with gases that enter and exits through ports. Generated 25 electrical current is taken off through terminals. The housing is produced from metal plates that are laser welded to provide a gas tight seal. US2002168560A Describes a base manifold for a modular solid 30 oxide fuel cell assembly which comprises a plurality of re ceiving areas for receiving a plurality of solid oxide fuel cell stacks; a fuel inlet passageway disposed between a WO 2013/053374 PCT/EP2011/005165 6 manifold fuel inlet port and a plurality of stack fuel inlet ports; an oxidant inlet passageway disposed between a manifold oxidant inlet port and a plurality of stack oxi dant inlet ports; a fuel outlet passageway disposed between 5 a plurality of stack fuel outlet ports and a manifold fuel outlet port; and an oxidant outlet passageway disposed be tween a plurality of stack oxidant outlet ports and a mani fold oxidant outlet port. 10 W010102815 discloses a fuel cell or electrolysis cell stack that has force distribution members with one planar and one convex shape applied to at least its top and bottom face and in one embodiment further to two of its side faces. A compressed mat and further a rigid fixing collar surrounds 15 the stack and force distribution members, whereby the stack is submitted to a compression force on at least the top and bottom face and potentially also to two side faces. The as sembly is substantially gas tight in an axial direction of the primarily oval or circular shape and can be fitted with 20 gas tight end plates to form robust gas inlet and outlet manifolds. US2003235743A A solid-oxide fuel cell stack having a plu rality of fuel cells connected in series and disposed as 25 two stacks side-by-side in head-to-tail configuration, con nected in series across one end and having cathode and an ode current collectors mounted side-by-side on a stack base at the other end. Each current collector is a flat plate extending from the stack footprint. Surrounding the stacks 30 is a cover-sealing flange so formed that when the cover is in place a thermal jacket is formed around the stacks. The current collectors are electrically insulated from the WO 2013/053374 PCT/EP2011/005165 7 sealing flange and cover by a gasket, and extend outwards from the flange for electrical attachment to a load. This arrangement permits the stacks to be fully assembled and the stack cover secured and sealed in place without need 5 for passing electrical leads through openings in the cover which must be subsequently sealed. US2010062297A describes an invention which relates to a de vice comprising a thermally insulating receptacle and, ar 10 ranged in the receptacle, at least one high-temperature fuel cell system component enclosed by at least one insu lating layer of a first material, a clamping means acting on the insulating layer. In accordance with the invention it is provided for that, the clamping means comprises, sup 15 ported by a receptacle housing and acting on the insulating layer, one or more-plate-shaped elements made of a second material which is elastically deformable at a contact pres sure, at which the first material is not deformable. 20 US2004072059 describes a container structure for a fuel cell comprises a fuel cell container, a separate plate hav ing a plurality of orifices, an exhaust pipe discharging gas in the fuel cell container, and a compressed air pipe sending a compressed air into the fuel cell container. In 25 the container structure, the inside of the fuel cell con tainer is divided into an exhaust manifold unit and a cell housing unit housing the fuel cell by the separate plate, the exhaust pipe is attached to connect an exhaust port provided on the exhaust manifold unit and an exhaust outlet 30 provided on a surface of a vehicle, an air pressure in the exhaust manifold unit is set at an atmospheric pressure, and an air pressure in the cell housing unit is set equal WO 2013/053374 PCT/EP2011/005165 8 to or smaller than a fuel cell gas pressure and equal to or larger than the atmospheric pressure by the compressed air pipe. 5 In spite of the presented known solutions to the compres sion, the enclosing and the interface problems of a fuel cell or electrolysis cell stack, none of them present an improved solution to all of the presented problems as does the present invention as described in the following. 10 It is an object of the present invention to solve the men tioned problems by providing a new SOFC or SOEC stack as sembly for at least one cell stack, suited for connection to a solid oxide fuel or electrolysis cell system. 15 In the following, the fuel cell stack will be regarded as a black box which generates electricity and heat when sup plied with oxidation gas and fuel gas. The function and in ternal components of the fuel cell stack is considered 20 known art and is not the subject of this invention. SOFC or SOEC stacks can have many physical shapes, not lim iting the present invention but for the reason of simplify ing the disclosure of the invention, the following explana 25 tion and examples will take as a starting point a cell stack with substantially a box shape i.e. with six rectan gular sides, eight corners and twelve edges placed in sub stantially rectangular connection three by three. In the following, the cell stack will thus be characterised.as 30 having a top face, a bottom face and a plurality of side faces. At least the top face and the bottom face need a compression force such that the top face is pressed towards WO 2013/053374 PCT/EP2011/005165 9 the bottom face. Optionally, further two opposing side faces of the stack need a compression force against each other and in some cases further two opposing side faces need a compression force against each other. The at least 5 one solid oxide fuel or electrolysis cell stack further comprises a fuel gas inlet, a fuel gas outlet, oxidant gas inlet and oxidant gas outlet. The SOFC or SOEC stack assem bly further comprises a rigid housing with one substan tially closed top end, one open bottom interface end oppo 10 site the substantially closed end and at least one side. The housing is substantially enclosing the at least one stack top face and the plurality of side faces, the open bottom interface end is adapted to be connected to an in terface counterpart of said solid oxide fuel or electroly 15 sis cell system and provides interface for fuel gas and oxidant gas between the at least one stack and the SOFC or SOEC system. To provide the necessary compression force for the at least one stack, there is at least one flexible com pression force mat positioned inside the housing between 20 the at least one stack top face and the substantially closed top end of the housing. The at least one flexible compression force mat may be both electrically isolating and thermally insulating. Further, at least one flexible fixation mat is positioned inside the housing between at 25 least one of the plurality of stack side faces and the at least one side of the housing. Also the at least one flexi ble fixation mat may be both electrically isolating and thermally insulating. 30 To fix the stack in the housing and to provide at least a part of the interface of the SOFC or SOEC stack assembly towards the SOFC or SOEC system, the assembly further com- WO 2013/053374 PCT/EP2011/005165 10 prises a flexible-interface-fixture positioned adjacent to the open bottom interface end of the housing. The flexible interface-fixture partly encloses the at least one stack within the housing and at least partly covers the bottom 5 face of the at least one stack. The flexibility of the flexible-interface-fixture is defined as being rigid enough to provide fixture of the at least one stack in the housing when the stack is not in operation, i.e. it can provide a counterforce against the stack which is pressed in a direc 10 tion out of the housing by the force from the compressed compression force mat; but still the flexible-interface fixture is sufficiently flexible to allow for transfer of at least a part of the compression force from the compres sion force mat through the at least one stack, further 15 through the flexible-interface-fixture and against the in terface counterpart of the SOFC or SOEC system when the at least one stack is in operation. Though it may seem difficult to achieve both these counter 20 acting objectives of flexibility contra rigidity, the task is considerably facilitated by the fact that there is a large difference between the temperature of the flexible interface-fixture when the at least one stack is in opera tion and when not in operation. A range of materials can 25 therefore provide the aforementioned characteristic, e.g. a metal plate is far more rigid at a temperature of circa 20 0 C than at a temperature of 800 0 C (examples). Some of the important inherent advantages of the invention as described above is that the thermal mass of the SOFC or SOEC stack 30 assembly can be significantly reduced by means of the flexible-interface-fixture which is relatively thin as com pared to known art interface base-plates and the number of WO 2013/053374 PCT/EP2011/005165 11 components is reduced since the compression force mat pro vides compression force of the at least one stack as well as packing force of the flexible-interface-fixture towards the SOFC or SOEC system interface counterpart. 5 In an embodiment of the invention the necessary flexibility is achieved by a flexible-interface-fixture with a flexural stiffness between 0,01 Nm (Nm being Newton meters) and 5000 Nm, preferably between 0,1 Nm and 1000 Nm, preferably be 10 tween and 1 Nm and 500 Nm at 20C temperature. This flexi bility ensures the necessary rigidity for fixing and com pressing the cell stack in the housing when not connected to an SOEC or SOFC system and at the same time ensures the necessary flexibility to transmit at least a part of the 15 compression force from the flexible compression force mat to the interface counterpart of the SOFC or SOEC system when in operation. The range of the flexural stiffness var ies off course with the demands of the actual cell stack and system, which may vary widely with stack size, stack 20 type and further parameters. The flexibility must therefore be chosen by the man skilled in the art by calculations of flexural stiffness in relation to the specific system de mands or even by iterative experiments. 25 In an embodiment of the invention as described in the fore going, the open bottom interface end of the housing and said flexible-interface-fixture are planar and has an ex ternal interface surface which is in substantially the same plane when connected to the interface counterpart of the 30 solid oxide fuel or electrolysis cell system. This makes the interface and the connection of the assembly to an SOFC or an SOEC system simple and reduces the manufacturing WO 2013/053374 PCT/EP2011/005165 12 costs. It is to be understood that since the flexible interface-fixture is subjected to the compression force of the compression force mat, the interface surface will not be plane when the assembly is not connected to the inter 5 face counterpart of an SOFC or an SOEC system. In a further embodiment of the invention, the connection of the assembly to an SOFC or an SOEC system is further sim plified by the provision of a flange at the open bottom in 10 terface end of the housing. The flange can be an integrated part of the housing (i.e. cast in one piece), it can be at tached to the housing in any known way such as welding, bracing, by screws or as also known as a loose flange, which acts against a mechanical stop or edge of the hous 15 ing. In any case, the flange is suited for connection to the interface counterpart of the SOFC or SOEC system. In a specific embodiment of the invention, the flexible interface-fixture is a steel plate (e.g. inconel, 253 MA 20 etc.) connected to the open bottom interface end of the housing. It can be attached to the housing by any known means such as welding, bracing, a mechanical fit etc. Fur ther the thickness of the steel plate can be chosen to spe cifically match the requirements for flexibility for a 25 given application. Applications may vary with size of the cell stack, number of cells, operating temperature, cell types etc. In an embodiment of the invention, the thickness of the flexible-interface-fixture is in the range of 0.1 5 mm, preferably in the range of 0.5 - 3 mm. The flexible 30 interface-fixture has a low thermal mass relative to known art housing base plates as it is thin and does not neces sarily cover the entire open bottom interface end of the WO 2013/053374 PCT/EP2011/005165 13 housing. When the cell stack is not in operation and the assembly is not connected to an interface counterpart of an SOFC or SOEC system, the open bottom interface end of the housing as well as the flexible-interface-fixture can be 5 covered by a protection cover, which covers the entire open bottom interface end of the housing and thereby protects the cell stack within the housing. In an embodiment, the protection cover can be rigid and adapted to fit the flange connection of the housing so that a tight fit to the hous 10 ing and compression of the cell stack is possible. In an embodiment of the invention, the compression force which is transmitted from the compression force mat, to the cell stack and further to the flexible-interface-fixture is 15 utilised to provide at least a part of a sealing force for a gasket which is provided between the bottom face of the at least one stack and the flexible-interface-fixture to provide a sealing between at least one fuel or oxidant gas inlet or outlet of the at least one stack and the flexible 20 interface-fixture when the assembly is connected to the in terface counterpart of said system and the at least one stack is in operation. The gasket ensures that each of the process gas connections to and from the at least one cell stack is gas tight such that the process gasses are not un 25 intentionally mixed which would reduce performance and po tentially also be dangerous or damaging. In an embodiment where the at least one cell stack has ex ternal manifolding for the oxidation gas and internal mani 30 folding for the fuel gas, this embodiment further ensures a well defined sealing pressure to the critical fuel gas, since this pressure is at least partly provided by the com- WO 2013/053374 PCT/EP2011/005165 14 pression force mat and therefore is less sensitive to the force by which the assembly is connected to the interface counterpart of the SOFC or an SOEC system. In this embodi ment one side face of the at least one stack has external 5 manifold oxidant gas inlet, one side face of the at least one stack has external manifold oxidant gas outlet and the bottom face of the at least one stack has internal manifold fuel gas inlet and internal manifold fuel gas outlet. 10 In yet a further embodiment of the invention, the at least one stack has external manifolding for both the oxidant gas inlet an outlet and the fuel gas inlet and outlet, and wherein the at least one flexible fixation mat provides a gas sealing between at least two of the gas inlets and out 15 lets of the at least one stack. This embodiment reduces ma terial costs and the number of components since the flexi ble fixation mat serves more purposes, fixation, gas seal ing and thermal insulation. 20 In another embodiment, the at least one stack can have in ternal manifolding for both the oxidant gas inlet and out let and the fuel gas inlet and outlet. The housing of the assembly can be made by any conventional 25 production method such as casting, deep-drawing, selective laser melting or welding, and it can be provided with stiffening and strengthening external and/or internal ribs. Further at least a part of these ribs can be adapted to provide flow guidance of at least a part of the oxidant or 30 fuel gasses. This can be advantageous to ensure an even distribution of the process gasses to and from the at least one cell stack.

WO 2013/053374 PCT/EP2011/005165 15 In a further embodiment of the invention, the stiffening and strengthening of the housing may be provided by pro files formed on at least one of the at least one sides of the housing. These profiles may serve more than this pur 5 pose as they can also provide space for further necessary elements of the assembly not mentioned in the above, such as current collectors. The materials for the at least one compression force mat 10 and also the at least one fixation mat may be, but is not restricted to, any of the following materials: ceramic, glass, metal or a combination of these, preferably porous calcium silicate or glass fibre reinforced calcium silicate or refractory ceramic fibre or glass fibre, preferably mag 15 nesia-silica fibre, alumina fibre with or without an amount of silica, low alkali aluminosilicate compositions contain ing one or more of the following oxides: zirconia, chromia or titania or vermiculite. 20 The invention as described has a range of advantages over the known art some of which are: - A rigid heavy base plate with a large thermal mass is simply omitted from the cell stack assembly. Instead the 25 rigid base and counterforce necessary for compression of the at least one stack and necessary to seal the assembly to a system interface counterpart is provided by that same system interface counterpart. Only a flexible-interface fixture of low thermal mass is provided to fix the at least 30 one stack in the housing when not in operation and/or not connected to a system interface counterpart.

WO 2013/053374 PCT/EP2011/005165 16 - All process gas connections are positioned on one in terface side of the cell stack assembly. In an embodiment this interface is a plane surface with a flange connection and the sealing pressure is well defined as it is provided 5 by the compression force mat. This makes the connection of the cell stack assembly to the system interface counterpart simple, secure and cost reducing. - The thermal mass of the housing is reduced by optimiz 10 ing the material use and the strength by the use of strengthening ribs and/or profiles. - The external manifolding which is an integrated part of the assembly provides a low pressure loss, thereby sav 15 ing energy and process gas blower capacity. At the same time the simplicity of the construction of the external manifolding is cost reducing and failure minimizing. - Leakage of process gas from the cell stack assembly is 20 minimized as the cell stack is enclosed by the housing on all sides except the interface side which is sealed to the interface counterpart. - The assembly is robust against rough handling and vi 25 brations as weak and protruding parts are omitted and the stack is enclosed by a shock-absorbing layer and a hard shell, same principle as a protective helmet. _ A low cost price is obtained by minimizing the number 30 of parts to save material cost and production/assembly time.

WO 2013/053374 PCT/EP2011/005165 17 Features of the Invention: 1. Solid oxide fuel or electrolysis cell stack assembly suited for connection to a solid oxide fuel or electrolysis cell system, said assembly comprising 5 e at least one solid oxide fuel or electrolysis cell stack, the at least one stack comprises a plurality of fuel cells or electrolysis cells, the at least one stack comprises a top face, a bottom face, a plurality of side-faces, fuel gas inlet, fuel gas outlet, oxi 10 dant gas inlet and oxidant gas outlet, e a rigid housing with one substantially closed top end, one open bottom interface end opposite the substan tially closed end and at least one side, the housing is substantially enclosing the at least one stack top 15 face and the plurality of side faces, the open bottom interface end is adapted to be connected to an inter face counterpart of said solid oxide fuel or elec trolysis cell system and provides interface for fuel gas and oxidant gas between the at least one stack and 20 said system, e at least one flexible compression force mat positioned inside the housing between the at least one stack top face and the substantially closed top end of the hous ing, the compression force mat provides compression 25 force for the at least one stack e at least one flexible fixation mat positioned inside the housing between at least one of the plurality of stack side faces and the at least one side of the housing, 30 wherein said assembly further comprises a flexible interface-fixture positioned adjacent to the open bottom interface end of the housing whereby it at least partly en- WO 2013/053374 PCT/EP2011/005165 18 closes the at least one stack within the housing and at least partly covers the bottom face of the at least one stack, said flexible-interface-fixture is rigid enough to provide fixture of the at least one stack in said housing 5 when the at least one stack is not in operation, but suffi ciently flexible to allow for transfer of at least a part of the compression force from the compression force mat through the at least one stack, further through the flexi ble-interface-fixture and against the interface counterpart 10 of the solid oxide fuel or electrolysis cell system when the at least one stack is in operation. 2. Solid oxide fuel or electrolysis cell stack assembly according to feature 1, wherein the flexural stiffness of 15 the flexible-interface-fixture is between 0,01 Nm and 5000 Nm, preferably between 0,1 Nm and 1000 Nm, preferably be tween and 1 Nm and 500 Nm at 20 0 C. 3. Solid oxide fuel or electrolysis cell stack assembly 20 according to any of the preceding features, wherein said open bottom interface end of the housing and said flexible interface-fixture are planar, parallel and has an external interface surface which is in substantially the same plane when connected to the interface counterpart of the solid 25 oxide fuel or electrolysis cell system. 4. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding features, wherein said open bottom interface end of the housing is provided with a 30 flange suited for connection to the interface counterpart of the system, said flange can be an integrated part of the housing, or it can be attached to the housing by means of WO 2013/053374 PCT/EP2011/005165 19 welding, bracing, screws or it can be a loose flange with a mechanical fit around the housing. 5. Solid oxide fuel or electrolysis cell stack assembly 5 according to any of the preceding features, wherein the flexible-interface-fixture is a steel plate connected to the open bottom interface end of the housing. 6. Solid oxide fuel or electrolysis cell stack assembly 10 according to any of the preceding features, wherein the flexible-interface-fixture is connected to the housing by means of welding, bracing, screws or a mechanical fit. 7. Solid oxide fuel or electrolysis cell stack assembly 15 according to any of the preceding features, wherein the thickness of the flexible-interface-fixture is in the range of 0.1 - 5 mm, preferably in the range of 0,5 - 3 mm. 8. Solid oxide fuel or electrolysis cell stack assembly 20 according to any of the preceding features, wherein the width of the flexible-interface-fixture corresponds to the inner width of the open bottom interface end of the hous ing, whereby the flexible-interface-fixture can be mounted inside said open bottom interface end of the housing. 25 9. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding features, wherein at least one gasket is provided between the bottom face of the at least one stack and the flexible-interface-fixture to 30 provide a sealing between at least one fuel or oxidant gas inlet or outlet of the at least one stack and the flexible interface-fixture, and wherein the pressure necessary to WO 2013/053374 PCT/EP2011/005165 20 provide a gas tight seal of said gasket is provided at least partly by the flexible compression force mat when the assembly is connected to the interface counterpart of said system and the at least one stack is in operation. 5 10. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding features, wherein the at least one stack has external manifolding for the oxidant gas and internal manifolding for the fuel gas, one side 10 face of the at least one stack has external manifold oxi dant gas inlet, one side face of the at least one stack has external manifold oxidant gas outlet and the bottom face of the at least one stack has internal manifold fuel gas inlet and internal manifold fuel gas outlet. 15 11. Solid oxide fuel or electrolysis cell stack assembly according to any of the features 1 - 8, wherein the at least one stack has external manifolding for both the oxi dant gas inlet and outlet and the fuel gas inlet and out 20 let, and wherein the at least one flexible fixation mat provides a gas sealing between at least two of the gas inlets and outlets of the at least one stack. 12. Solid oxide fuel or electrolysis cell stack assembly 25 according to any of the features 1 - 8, wherein the at least one stack has internal manifolding for both the oxi dant gas inlet and outlet and the fuel gas inlet and out let. 30 13. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding features, wherein the housing is made by casting, deep-drawing, laser sintering WO 2013/053374 PCT/EP2011/005165 21 or welding, and wherein the housing is provided with stiff ening and strengthening external and/or internal ribs. 14. Solid oxide fuel or electrolysis cell stack assembly 5 according to feature 13, wherein the housing at least has internal stiffening and strengthening ribs, and wherein at least a part of said ribs are adapted to provide flow guid ance of at least a part of the oxidant or fuel gasses. 10 15. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding features, wherein at least one of the at least one side of the housing is formed as at least one stiffening and strengthening profile. 15 16. Solid oxide fuel or electrolysis cell stack assembly according to feature 14, wherein at least one of said pro file(s) provide space for further elements of the assembly such as current collectors. 20 17. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding features, wherein the at least one compression force mat and the at least one fixa tion mat is made from one or more of the following materi als: of ceramic, glass, metal or a combination of these, 25 preferably porous calcium silicate or glass fibre rein forced calcium silicate or refractory ceramic fibre or glass fibre, preferably magnesia-silica fibre, alumina fi bre with or without an amount of silica, low alkali alumi nosilicate compositions containing one or more of the fol 30 lowing oxides: zirconia, chromia or titania or vermiculite.

WO 2013/053374 PCT/EP2011/005165 22 Particular embodiments of the invention are further illus trated by the accompanying drawings showing examples of em bodiments of the invention. 5 Fig. 1 shows an isometric bottom end view of the cell stack assembly according to an embodiment of the invention. Fig. 2 shows a cut side view of the cell stack assembly ac cording to an embodiment of the invention. 10 Fig. 3 shows an isometric top end view of the cell stack assembly according to an embodiment of the invention. Fig. 4 shows an cut side view of the cell stack assembly according to an embodiment of the invention. 15 Fig. 5A shows an cut side view of the cell stack assembly as shown on Fig. 5B according to an embodiment of the in vention. 20 Fig. 6 shows a cut side view of the cell stack assembly when mounted on an SOFC or SOEC system according to an em bodiment of the invention.

WO 2013/053374 PCT/EP2011/005165 23 Position Number Overview: 100, 200, 300, 400, 500 and 600: Cell stacks assembly (SOFC or SOEC). 101, 201, 301, 401, 501, 601: Housing. 5 102, 202, 302, 402, 502, 602: Flange. 103, 203, 403, 503, 603: Cell Stack (SOFC or SOEC). 104, 204, 404, 504, 604: Flexible-interface-fixture. 105, 505: Oxidant gas outlet. 106, 506: Oxidant gas inlet. 10 107, 507: Fuel gas inlet. 108, 508: Fuel gas outlet. 209, 409, 509, 609: Gasket. 110, 210, 410, 610: Flexible fixation mat. 211, 411, 511, 611: Flexible compression force 15 mat. 112, 312, 412, 512, 612: Stiffening and strengthening ribs. 650: SOFC or SOEC system. 652: System flange. 20 659: System gasket. Referring to Fig. 1, one embodiment of a fuel cell stack assembly (100) is shown. A housing (101) is shown with the open bottom interface end upwards. This end is provided 25 with a flange (102) so the cell stack assembly can be con nected to an interface counterpart of an SOFC system (not shown) in a simple, safe and gas tight manner. The fuel cell stack (103) is positioned in the housing, 30 fixed in position by two flexible fixation mats (110) lo cated inside the housing, one between one side of the hous ing and the adjacent side face of the fuel cell stack and WO 2013/053374 PCT/EP2011/005165 24 the other located between the opposite side of the housing and its adjacent side face of the fuel cell stack. In this manner the fuel cell stack is squeezed between the two flexible fixation mats and thereby at least to some extent 5 kept in position by the friction forces. The fuel cell stack is further fixed in its position in the housing by the flexible compression force mat (not shown) located in side the housing between the top end and the top face of the fuel cell stack. The compression force mat presses the 10 fuel cell stack towards the opposite open bottom interface end of the housing where the flexible-interface-fixture (104) in form of a thin steel plate is reacting to the com pression force with a counter-force is to some extent bend outwards because of its flexibility. In this embodiment, 15 the flexible-interface-fixture has a width corresponding to the inside width of the flange. As shown on Fig. 1, the fuel cell stack is not in operation and therefore the flexibility of the flexible-interface-fixture plate is thus relative small as compared to the operation state where the 20 temperature is considerably higher. The fuel cell stack of the embodiment shown in Fig. 1 is a combined external (air) and internal (fuel) manifolded stack. Oxidant gas such as ambient air is led to the side 25 manifolded oxidant gas inlet of the fuel cell stack via the oxidant gas inlet (106) and is led away from the fuel cell stack via the oxidant gas outlet (105). The assembly is simple and robust in its construction since no actual ex ternal manifolds are necessary: The flexible fixation mats 30 not only fix the fuel cell stack, but also ensures a gas tight seal between the housing side and the fuel cell stack, hence the external manifolds are constituted by the WO 2013/053374 PCT/EP2011/005165 25 void between the side of the housing and the external mani fold sides of the fuel cell stack. Fuel is led to and from the fuel cell stack via the fuel gas inlet (107) and the fuel gas outlet (108). As can be seen, all process gas con 5 nections are located on the same side of the assembly, the interface end of the housing. The interface as shown is a plane surface where the flange side and the external side of the flexible-interface-fixture are located in the same plane. The housing and the flange is stiffened by the 10 stiffening and strengthening ribs (112) which make it pos sible to reduce the thickness of both the housing walls and the flange and thus the thermal mass and the material costs. 15 Turning to Fig. 2, the same embodiment of the invention is now shown in a cut side view of the assembly, which enables the showing of the flexible compression force mat (211). It is visible that a fuel gas gasket (209) is located between the fuel cell stack (203) top face and the flexible 20 interface-fixture (204). The flexible-interface-fixture is here shown plane. As mentioned, it is more flexible and therefore more forces transferring when in operation, but still a slight, not shown, bend is possible also when not in operation. The fuel gasket is compressed by the compres 25 sion force from the flexible compression force mat. As men tioned, flexible fixation mats (210) are located between two of the fuel cell stack side faces and two of the hous ing (201) sides to ensure fixation and gas sealing between the oxidation gas inlet side and the oxidation gas outlet 30 side. In this embodiment, the housing has an indent at the open bottom interface end for location of the flexible interface-fixture.

WO 2013/053374 PCT/EP2011/005165 26 On Fig. 3 the external top end of the housing (301) is visible as well as two of the housing sides. The housing and the flange (302) for connection to a SOFC system inter face counterpart is integrated, as is the stiffening and 5 strengthening ribs (312). This embodiment can have cast steel housing. Not shown are the current collectors, which provides the electrical power output from the fuel cell. The terminals for the current collectors can be located on the top end of the housing. But other locations of the cur 10 rent terminals, such as the sides or the interface side of the assembly (to keep all connections on the same side) are also possible. Fig. 4 shows a cut side view of the assembly (400) as in 15 Fig. 2, but here the deflection of the flexible-interface fixture (404) is shown. The flexible-interface-fixture is in this embodiment a steel plate. It is exposed to a force from the flexible compression force mat (411) via the cell stack (403) and the gasket (409), and as the thermal mass 20 of the plate is kept low, the force bends the plate. As seen on Fig. 4, the housing (401) has in this embodiment no indent for location of the plate. In stead the plate fits inside the housing and can be welded in a position where the surface of the flexible-interface-fixture is plane with 25 the flange (402) as shown. Also two flexible fixation mats (410) is shown as is a stiffening and strengthening rib (412) which goes around two sides and the closed top end of the housing. The stiffening and strengthening ribs also serves to lower the thermal mass of the housing as compared 30 to housing without ribs and thus the necessity for thicker walls and the ribs can serve as cooling ribs for the hous ing.

WO 2013/053374 PCT/EP2011/005165 27 In Fig. 5A a side cut view of the cell stack assembly (500) in Fig. 5B is shown. The cut is made where the deflection of the flexible-interface-fixture (504) due to the force from the flexible compression force mat (511) is at its 5 maximum and therefore the distance from the surface of the flange (502) to the surface of the flexible-interface fixture is quite visible in the cut. Between the flexible interface-fixture and the cell stack (503) is a sealing gasket (509). The cell stack of this embodiment is a co 10 flow stack, which means that the oxidant gas flow direction is the same as the fuel gas flow direction, in this case from left to right in Fig 5A. Hence the oxidant gas inlet (506) and the fuel gas inlet (507) is located in the left side of the assembly and the oxidant gas outlet (505) and 15 the fuel gas outlet (508) is located in the right side of the assembly. As seen on Fig. 5A, the cell stack is a com bined internal and external manifolded stack: the fuel gas side (anode) of the stack has internal manifolding and the oxidant gas side (cathode) of the stack has external mani 20 folding. According to the invention the external manifolds are simply the void between the cell stack and the housing (501). Some of the stiffening and strengthening ribs (512) are round-going on two sides and the closed top end of the housing, whereas others are located only adjacent to the 25 flange. They serve to stiffen and strengthen the housing but also to stiffen and strengthen the flange, which other wise should have been made in larger dimensions. Hence the thermal mass is kept low. 30 In Fig. 6 the cell stack assembly (600) is shown in side cut view with the interface connected to an SOFC or SOEC system (650) to illustrate how the flexible-interface- WO 2013/053374 PCT/EP2011/005165 28 fixture ((604) is plane and in the same plane as the flange (602) when the flange (602) is connected to the system flange (652) and at least a part of the force from the flexible compression force mat (611) is countered by the 5 connection/packing force from the system flange. As de scribed, the force from the flexible compression force mat is transmitted to the flexible-interface-fixture via the cell stack (603) whereby it provides both a sealing force to the gaskets as well as a stack compression force. Apart 10 from the gasket (609) already described in the foregoing, also a system gasket (659) is shown, both gaskets providing sealing between the flanges and the gas connections. Hence, because of the flexible nature of the flexible-interface fixture, a large thermal mass is omitted since the counter 15 pressure is provided by the connected system, which in any case needs to be rigid enough to provide a sealing force. The side cut on Fig. 6 also shows the two flexible fixation mats (610) between the cell stack and the housing (601) which serves to fix the stack in the correct position and 20 provides gas seal between the oxidation gas inlet and out let side of the cell stack. A stiffening and strengthening rib (612) as explained before is also shown. Examples 25 For a SOFC stack with the cell dimensions 120 x 120 mm cal culations were made for a flexible-interface-fixture in the form of a steel plate with a thickness of 0.1 mm and 5 mm: Flexural stiffness of the flexible-interface-fixture. The 30 stiffness is based on the plate equation: WO 2013/053374 PCT/EP2011/005165 29 D=Exh' 12(1-v 2 ) E = 200.000 N2 mm v=0.31 h = 0.1mm D, =0.02Nm h 2 =5mm D2= 2304.83Nm Where E is the elastic modulus for the chosen steel plate, h is the thickness of the steel plate and v is the Pois 5 son's ratio. Experiments were done with a flexible-interface-fixture thickness of 3 mm showing both satisfying cell stack com pression and sealing.

Claims

1. Solid oxide fuel or electrolysis cell stack assembly suited for connection to a solid oxide fuel or electrolysis 5 cell system, said assembly comprising e at least one solid oxide fuel or electrolysis cell stack, the at least one stack comprises a plurality of fuel cells or electrolysis cells, the at least one stack comprises a top face, a bottom face, a plurality 10 of side faces, fuel gas inlet, fuel gas outlet, oxi dant gas inlet and oxidant gas outlet, e a rigid housing with one substantially closed top end, one open bottom interface end opposite the substan tially closed end and at least one side, the housing 15 is substantially enclosing the at least one stack top face and the plurality of side faces, the open bottom interface end is adapted to be connected to an inter face counterpart of said solid oxide fuel or elec trolysis cell system and provides interface for fuel 20 gas and oxidant gas between the at least one stack and said system, e at least one flexible compression force mat positioned inside the housing between the at least one stack top face and the substantially closed top end of the hous 25 ing, the compression force mat provides compression force for the at least one stack e at least one flexible fixation mat positioned inside the housing between at least one of the plurality of stack side faces and the at least one side of the 30 housing, wherein said assembly further comprises a flexible interface-fixture positioned adjacent to the open bottom WO 2013/053374 PCT/EP2011/005165 31 interface end of the housing whereby it at least partly en closes the at least one stack within the housing and at least partly covers the bottom face of the at least one stack, said flexible-interface-fixture is rigid enough to 5 provide fixture of the at least one stack in said housing when the at least one stack is not in operation, but suffi ciently flexible to allow for transfer of at least a part of the compression force from the compression force mat through the at least one stack, further through the flexi 10 ble-interface-fixture and against the interface counterpart of the solid oxide fuel or electrolysis cell system when the at least one stack is in operation.

2. Solid oxide fuel or electrolysis cell stack assembly 15 according to claim 1, wherein the flexural stiffness of the flexible-interface-fixture is between 0,01 Nm and 5000 Nm, preferably between 0,1 Nm and 1000 Nm, preferably between and 1 Nm and 500 Nm at 20 0 C. 20

3. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein said open bottom interface end of the housing and said flexible interface-fixture are planar, parallel and has an external interface surface which is in substantially the same plane 25 when connected to the interface counterpart of the solid oxide fuel or electrolysis cell system.

4. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein said open 30 bottom interface end of the housing is provided with a flange suited for connection to the interface counterpart of the system, said flange can be an integrated part of the WO 2013/053374 PCT/EP2011/005165 32 housing, or it can be attached to the housing by means of welding, bracing, screws or it can be a loose flange with a mechanical fit around the housing.

5 5. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the flexible-interface-fixture is a steel plate connected to the open bottom interface end of the housing. 10

6. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the flexible-interface-fixture is connected to the housing by means of welding, bracing, screws or a mechanical fit. 15

7. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the thickness of the flexible-interface-fixture is in the range of 0.1 - 5 mm, preferably in the range of 0,5 - 3 mm. 20

8. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the width of the flexible-interface-fixture corresponds to the inner width of the open bottom interface end of the housing, whereby the flexible-interface-fixture can be mounted in 25 side said open bottom interface end of the housing.

9. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein at least one gasket is provided between the bottom face of the at 30 least one stack and the flexible-interface-fixture to pro vide a sealing between at least one fuel or oxidant gas inlet or outlet of the at least one stack and the flexible- WO 2013/053374 PCT/EP2011/005165 33 interface-fixture, and wherein the pressure necessary to provide a gas tight seal of said gasket is provided at least partly by the flexible compression force mat when the assembly is connected to the interface counterpart of said 5 system and the at least one stack is in operation.

10. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the at least one stack has external manifolding for the oxidant 10 gas and internal manifolding for the fuel gas, one side face of the at least one stack has external manifold oxi dant gas inlet, one side face of the at least one stack has external manifold oxidant gas outlet and the bottom face of the at least one stack has internal manifold fuel gas inlet 15 and internal manifold fuel gas outlet.

11. Solid oxide fuel or electrolysis cell stack assembly according to any of the claims 1 - 8, wherein the at least one stack has external manifolding for both the oxidant gas 20 inlet and outlet and the fuel gas inlet and outlet, and wherein the at least one flexible fixation mat provides a gas sealing between at least two of the gas inlets and out lets of the at least one stack. 25

12. Solid oxide fuel or electrolysis cell stack assembly according to any of the claims 1 - 8, wherein the at least one stack has internal manifolding for both the oxidant gas inlet and outlet and the fuel gas inlet and outlet. 30

13. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the hous ing is made by casting, deep-drawing, selective laser melt- WO 2013/053374 PCT/EP2011/005165 34 ing or welding, and wherein the housing is provided with stiffening and strengthening external and/or internal ribs.

14. Solid oxide fuel or electrolysis cell stack assembly 5 according to claim 13, wherein the housing at least has in ternal stiffening and strengthening ribs, and wherein at least a part of said ribs are adapted to provide flow guid ance of at least a part of the oxidant or fuel gasses. 10 15. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein at least one of the at least one side of the housing is formed as at least one stiffening and strengthening profile. 15 16. Solid oxide fuel or electrolysis cell stack assembly according to claim 14, wherein at least one of said pro file(s) provide space for further elements of the assembly such as current collectors. 20 17. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the at least one compression force mat and the at least one fixa tion mat is made from one or more of the following materi als: of ceramic, glass, metal or a combination of these, 25 preferably porous calcium silicate or glass fibre rein forced calcium silicate or refractory ceramic fibre or glass fibre, preferably magnesia-silica fibre, alumina fi bre with or without an amount of silica, low alkali alumi nosilicate compositions containing one or more of the fol 30 lowing oxides: zirconia, chromia or titania or vermiculite. WO 2013/053374 PCT/EP2011/005165 35 AMENDED CLAIMS received by the International Bureau on 30 August 2012 (30.08.12) 1. Solid oxide fuel or electrolysis cell stack assembly (100, 200, 300, 400, 500, 600) suited for connection to a solid oxide fuel or electrolysis cell system, said assembly comprising " at least one solid oxide fuel or electrolysis cell stack (103, 203, 403, 503, 603), the at least one stack comprises a plurality of fuel cells or electrolysis cells, the at least one stack comprises a top face, a bottom face, a plurality of side faces, fuel gas inlet (107, 507), fuel gas outlet (108, 508), oxidant gas inlet (106, 506) and oxidant gas outlet (105, 505), " a rigid housing (101, 201, 301, 401, 501, 601)with one closed top end, one open bottom interface end opposite the closed end and at least one side, the housing is enclosing the at least one stack top face and the plurality of side faces, the open bottom interface end is adapted to be connected to an interface counterpart of said solid oxide fuel or electrolysis cell system and provides interface for fuel gas and oxidant gas between the at least one stack and said system, e at least one flexible compression force mat (211, 411, 511, 611) positioned inside the housing between the at least one stack top face and the closed top end of the housing, the compression force mat provides compression force for the at least one stack " at least one flexible fixation mat (110, 210, 410, 610) positioned inside the housing between at least one of the AMENDED SHEET (ARTICLE 19) WO 2013/053374 PCT/EP2011/005165 36 plurality of stack side faces and the at least one side of the housing, wherein said assembly further comprises a flexible-interface fixture (104, 204, 404, 504, 604) positioned adjacent to the open bottom interface end of the housing whereby it at least partly encloses the at least one stack within the housing and at least partly covers the bottom face of the at least one stack, wherein the thickness of the flexible-interface-fixture is in the range of 0.1 - 3 mm, said flexible-interface-fixture has a flexural stiffness of between 0,01 Nm and 5000 Nm, whereby it is rigid enough to provide fixture of the at least one stack in said housing when the at least one stack is not in operation, but sufficiently flexible to allow for transfer of at least a part of the compression force from the compression force mat through the at least one stack, further through the flexible-interface-fixture and against the interface counterpart of the solid oxide fuel or electrolysis cell system when the at least one stack is in operation. 2. Solid oxide fuel or electrolysis cell stack assembly according to claim 1, wherein the flexural stiffness of the flexible-interface-fixture is between 0,1 Nm and 1000 Nm, preferably between 1 Nm and 500 Nm at 20 0 C. 3. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein said open bottom interface end of the housing and said flexible-interface-fixture are planar, parallel and has an external interface surface which is in the same plane when connected to the interface counterpart of the solid oxide fuel or electrolysis cell system. 4. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein said open bottom AMENDED SHEET (ARTICLE 19) WO 2013/053374 PCT/EP2011/005165 37 interface end of the housing is provided with a flange (102, 202, 302, 402, 502, 602) suited for connection to the interface counterpart of the system, said flange can be an integrated part of the housing, or it can be attached to the housing by means of welding, bracing, screws or it can be a loose flange with a mechanical fit around the housing. 5. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the flexible interface-fixture is a steel plate connected to the open bottom interface end of the housing. 6. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the flexible interface-fixture is connected to the housing by means of welding, bracing, screws or a mechanical fit. 7. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the width of the flexible-interface-fixture corresponds to the inner width of the open bottom interface end of the housing, whereby the flexible interface-fixture can be mounted inside said open bottom interface end of the housing. 8. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein at least one gasket (209, 409, 509, 609) is provided between the bottom face of the at least one stack and the flexible-interface-fixture to provide a sealing between at least one fuel or oxidant gas inlet or outlet of the at least one stack and the flexible-interface fixture, and wherein the pressure necessary to provide a gas tight seal of said gasket is provided at least partly by the flexible compression force mat when the assembly is connected to the AMENDED SHEET (ARTICLE 19) WO 2013/053374 PCT/EP2011/005165 38 interface counterpart of said system and the at least one stack is in operation. 9. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the at least one stack has external manifolding for the oxidant gas and internal manifolding for the fuel gas, one side face of the at least one stack has external manifold oxidant gas inlet, one side face of the at least one stack has external manifold oxidant gas outlet and the bottom face of the at least one stack has internal manifold fuel gas inlet and internal manifold fuel gas outlet. 10. Solid oxide fuel or electrolysis cell stack assembly according to any of the claims 1 - 7, wherein the at least one stack has external manifolding for both the oxidant gas inlet and outlet and the fuel gas inlet and outlet, and wherein the at least one flexible fixation mat provides a gas sealing between at least two of the gas inlets and outlets of the at least one stack. 11. Solid oxide fuel or electrolysis cell stack assembly according to any of the claims 1 - 7, wherein the at least one stack has internal manifolding for both the oxidant gas inlet and outlet and the fuel gas inlet and outlet. 12. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the housing is made by casting, deep-drawing, selective laser melting or welding, and wherein the housing is provided with stiffening and strengthening external and/or internal ribs (112, 312, 412, 512, 612). 13. Solid oxide fuel or electrolysis cell stack assembly according to claim 12, wherein the housing at least has internal AMENDED SHEET (ARTICLE 19) WO 2013/053374 PCT/EP2011/005165 39 stiffening and strengthening ribs, and wherein at least a part of said ribs are adapted to provide flow guidance of at least a part of the oxidant or fuel gasses. 14. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein at least one of the at least one side of the housing is formed as at least one stiffening and strengthening profile.

15. Solid oxide fuel or electrolysis cell stack assembly according to claim 13, wherein at least one of said profile(s) provide space for further elements of the assembly such as current collectors.

16. Solid oxide fuel or electrolysis cell stack assembly according to any of the preceding claims, wherein the at least one compression force mat and the at least one fixation mat is made from one or more of the following materials: of ceramic, glass, metal or a combination of these, preferably porous calcium silicate or glass fibre reinforced calcium silicate or refractory ceramic fibre or glass fibre, preferably magnesia-silica fibre, alumina fibre with or without an amount of silica, low alkali aluminosilicate compositions containing one or more of the following oxides: zirconia, chromia or titania or vermiculite. AMENDED SHEET (ARTICLE 19)